Nano-Scaled TiO ₂ Interlayer Thickness as a Key Factor in the Dielectric and Electrical Performance of Spin-Coated Si-Based MIS Structures

This study systematically investigates the influence of TiO2 interlayer thickness on the electrical and dielectric properties of Al/TiO2/p-Si metal/insulator/semiconductor (MIS) structures. TiO2 thin films with precisely controlled thicknesses (29, 40.6, 159, 278.7, and 390 nm) were deposited onto [100]-oriented p-Si substrates via spin-coating, and cross-sectional FE-SEM analysis confirmed the uniformity and exact thickness of each layer. The X-ray diffraction analysis performed on all samples confirmed the prominent formation of the anatase phase of TiO2 in every sample. Capacitance, conductance, dielectric permittivity, dielectric loss, electrical modulus, and impedance measurements were performed to assess the effect of varying TiO2 thickness on device performance. The results reveal that increasing TiO2 thickness systematically modifies the flat-band voltage, interface trap density, and series resistance, while thicker layers introduce complex grain and grain-boundary contributions requiring multielement equivalent circuits for accurate impedance modeling. It has been found that TiO2 interlayer thicknesses at the nanometer scale are critical for optimizing the performance of Al/TiO2/p-Si/Al devices. The 40 nm (T2) sample yielded the best results and highlighted the importance of nanoengineered dielectric layers. Notably, films around 40 nm exhibit an optimal balance of high capacitance, balanced dielectric behavior, and favorable conductivity, highlighting the critical role of interlayer thickness in tuning electrical-dielectric behavior. This work provides valuable insights for the design of MIS devices, emphasizing how precise control of TiO2 thickness can optimize device performance and reliability in electronic applications.